Elevators typically have one car and one counterweight traveling vertically in a hoistway. These elevators have a suspension roping for suspending the elevator car and the counterweight on opposite sides of a rotatable rope wheel. The suspension roping passes around the rope wheel, which is mounted on a fixed location, whereby the ropes can take support from the rope wheel for suspending the elevator car and counterweight. The drawback of this kind of elevator is that in some cases it cannot utilize the hoistway space optimally in terms of transport capacity. For example, the lower parts of the hoistway are not available for people flow when the car is at the top end of the hoistway. Generally, the higher the hoistway is, the less efficiently the elevator provided with only one elevator car can utilize the whole height thereof. This drawback has been solved in prior art by placing two independent elevators on top of each other in the same (i.e. common) hoistway. Thus, one of them can serve the bottom floors and the other can serve the top floors. The drawback of this kind of elevator system is that it requires two hoisting machines and two ropings, which makes the elevator system expensive and difficult to modify later. Also, usually it is necessary to form a space vertically between the elevators for accommodating the hoisting machine of the lower one of the elevators, which makes it difficult to serve the floors between the elevators. It would be advantageous if the elevator system could be formed without multiple hoisting means for moving the two elevator cars, such as with only one hoisting machine and/or only one hoisting roping. This, however, has not been feasible in practice for great lifting heights, because the cars tend to be positioned irregularily relative to the landing that they stop. In particular, it has been difficult to position the two cars suspended by a common roping so that they are level with their landings simultaneously. Said irregularities have necessitated complicated adjustment devices of great adjustment ranges for carrying out the adjustment of position of the elevator cars so that they are level with a landing simultaneously.